1. Field of the Invention
The present invention relates to a switching device having an indexing bolt and a latching spring in which the indexing bolt is movably mounted in the direction of its longitudinal extension in an indexing bolt housing and in which the latching spring retains and axially biases the indexing bolt against a switch plate.
2. Background Art
Arrangements having an indexing bolt movably mounted in the direction of its longitudinal extension in an indexing bolt housing are used to display switching points in electrical switching devices. The indexing bolt itself is guided and held against a switch plate in such a switching device. The indexing bolt retained against the switch plate is spring loaded. To this end, a spring element is arranged between the indexing bolt and the indexing bolt housing. Typically, an indexing bolt is a cylindrical shaft having a conically tapered free end which forms a tip for engaging the switch plate. The indexing bolt housing is designed based upon the cylindrical shape of the indexing bolt shaft and generally has a cylindrical guide channel.
To ensure that the indexing bolt can be smoothly guided against the switch plate and that the switching position can be fixed in specific switching points near the switch plate, it is important that the indexing bolt is able to move in a longitudinal axial direction the channel of the indexing bolt housing even when transverse forces are acting on the indexing bolt during an activation of the switching device. However, this can only be accomplished by mounting the indexing bolt in the indexing bolt housing with the most optimal play possible.
If the play between the indexing bolt and the indexing bolt housing is too low, there is a risk that the indexing bolt will become jammed in the indexing bolt housing. If the play between the indexing bolt and indexing bolt housing is too high, the problem of the indexing bolt becoming jammed in the indexing bolt housing is at least largely prevented, but a switching device equipped with such an arrangement exhibits a level of play upon activation of the switching device that sometimes precludes a reliable switching. In general, it is undesirable to use switching devices whose operating lever (i.e., indexing bolt) has excessive play to ensure that the switching device is functional while switching.
To avoid these disadvantages, indexing bolts have been developed that carry a Teflon(copyright) ring for guiding the indexing bolt in the indexing bolt housing in the area of a thickened cylindrical material in order to reduce friction, and hence forestall jamming. The indexing bolt itself is made out of metal so that a moisture-induced swelling otherwise encountered with plastic cannot take place. However, such an indexing bolt is difficult to manufacture because the interacting components are only to have minimal tolerances. In unfavorable cases, the indexing bolt is rigidly guided in the indexing bolt housing. This could be countered through the use of springs with a correspondingly strong design.
Proceeding from this described background art, an object of the present invention is therefore to further develop the switching device of the described background art in such a way that the indexing bolt can be guided in the indexing bolt housing without jamming and with the least possible play using means that are easy to manufacture.
This object is achieved according to the present invention in that the indexing bolt of the switching device has several guiding means distributed along its periphery. The guiding means project outwardly from the indexing bolt and abut the surface of the guide channel of the indexing bolt housing in a radially biased manner.
In a first embodiment of the switching device in accordance with the present invention, the guiding means are formed by flexible guiding ribs that are arranged in the longitudinal direction of the indexing bolt. The guiding ribs guide the front area of the indexing bolt near its tip in the indexing bolt housing. The guiding ribs are preferentially spaced apart at the same angular distance relative to one another and abut the inner surface of the indexing bolt housing in order to guide the indexing bolt along the guide channel of the indexing bolt housing. The guiding ribs have a relatively small contact region which contacts the inner surface of the indexing bolt housing formed by the guide channel. Each guiding rib preferentially contacts the adjacent inner surface of the indexing bolt housing only along a respective contact line. The guiding ribs have flexible characteristics, and to some extent elastic characteristics, which result from the flexibility and elasticity characteristics of the material used to form the guiding ribs.
The guiding area near the tip of the indexing bolt exiting the indexing bolt housing is configured to guide the indexing bolt in the indexing bolt housing without play. Providing flexible guiding ribs that abut the inside of the indexing bolt housing ensures that at least this guiding section of the indexing bolt is guided without play.
In order to manufacture the indexing bolt, which is preferentially provided as a single piece, the guiding ribs can be oversized somewhat relative to the inside diameter of the guide channel located in the indexing bolt housing owing to their flexible characteristics. In cases where the indexing bolt is made out of a plastic material, e.g., in an injection molding process, the guiding ribs initially inserted in the indexing bolt housing under a certain level of bias can relax after some time, thereby equalizing a somewhat tighter initial fit after several activations of the indexing bolt. The plastic material has specific elastic characteristics in addition to the flexible characteristics of the guiding ribs fabricated from the plastic material. This ensures that the guiding ribs abut the inner surface of the indexing bolt housing formed by the guide channel at all times under a low level of bias.
In a second embodiment of the switching device in accordance with the present invention, the guiding means are movable pressure arms designed as levers. Each pressure arm has a deflecting element that interacts with the latching spring in such a way as to press the respective pressure arm in a radial direction against the inner surface of the indexing bolt housing. As a result, the indexing bolt includes an integrated, spring-loaded spreading mechanism. The spreading mechanism is designed to radially press the elastic pressure arms located in the area near the tip of the indexing bolt against the inner wall of the indexing bolt housing in response to the elastic force exerted by the latching spring. An advantage of the second embodiment is that the pressure force exerted by the pressure arms is always at least approximately proportional to the elastic force exerted by the latching spring. As such, the pressure force can be adjusted in a controlled and calculated manner via the structural design of the pressure arms and/or the selection of a suitable latching spring.
Both embodiments of the present invention provide that the guiding means are arranged in a first guiding section located near the shaft tip (i.e., bolt tip), and that another guiding section is situated at the end of the indexing bolt lying opposite the shaft tip. The indexing bolt is then guided in the indexing bolt housing via these two guiding sections. The second guiding section is preferably designed in such a way that the guiding means of the second guiding section exhibit a bead. The bead is preferentially rounded. In cases where the guiding means are to be somewhat elastic this end of the indexing bolt can be slotted with the slot intersecting the bead. Regardless of how the guiding means are designed in the rear guiding section, the elastic characteristics of the guiding means arranged in the area of the indexing bolt tip effectively prevent the indexing bolt from becoming jammed in the indexing bolt housing.